While the recent years have seen a use of an optical disk as a storage medium for a large-volume data file, music, video and the like, there still is an ongoing endeavor to increase a capacity of an optical disk in an attempt to use optical disks for an even more diversified applications.
A method generally used for efficient accessing of a large-capacity optical disk is to divide recording data into sectors having a data size of a constant unit or to record and reproduce using such sectors as a basic rewrite unit.
As for the sectors which serve as the basic rewrite unit, an address for identifying a sector is added to each sector.
A prior art optical disk having such a sector structure will now be described with reference to FIG. 23 which schematically shows a structure of this optical disk.
Part (a) of FIG. 23 shows a general overall structure of an optical disk according to a prior art example 1.
In part (a) of FIG. 23, denoted at 2301 is an optical disk substrate of polycarbonate, denoted at 2302 is a recording film, denoted at 2303 is a first recording track, denoted at 2304 is a second recording track, denoted at 2305 are zones which are provided by dividing the disk in accordance with a distance along the radius direction, denoted at 2307 are addresses for identification of sectors, and denoted at 2308 is a data recording area for recording data.
In the description on embodiments and the claims, “data” and “information” have the same meaning.
In part (a) of FIG. 23, a recording track is one recording track formed in the shape of a spiral which runs from an inner round toward an outer round of the optical disk, and the recording track contains the first recording track 2303 and the second recording track 2304. The first recording track 2303 and the second recording track 2304 each has the length equivalent to one round and alternate each round.
For the purpose of increasing the density along the direction of the tracks, the optical disk shown in FIG. 23 uses the land/group method which requires to use both a ditch portion for guiding the tracks (groove portion) and an inter-ditch portion (land portion) as a data recording area.
The data recording area 2308 is divided into a plurality of zones 2305 in accordance with a distance along the radius direction-of the optical disk, to thereby improve the recording density of the disk. In each zone, the addresses 2307 are aligned along the radius direction of the optical disk. In part (a) of FIG. 23, there are areas which are aligned along the radius direction and have different sector numbers, and the data recording area 2308 is divided into the two zones 2305. The data recording area 2308 may be divided into any desired number of zones. Hence, a sector which has a distance from the front edge of the address 2307 until the front edge of the next address 2307 remains at the same angle (an angle on polar coordinates whose origin is the center of the optical disk) in each zone.
The angle of the sector in the inner zone is larger than the angle of the sector in the outer zone. This sets the sector's average linear density in the inner zone approximately the same as the sector's average linear density in the outer zone.
The “linear density” means the volume of information recorded over a unit length in the recording track. The method described above which requires to provide a plurality of zones on a disk and change the angles of sectors in each zone to thereby ensure that average line densities of the respective zones become approximately constant within the disk is called the ZCAV method (Zoned Constant Angular Velocity method for recording or reproducing at a constant angular velocity) or the ZCLV method (Zoned Constant Linear Velocity method for recording or reproducing at a constant number of revolutions within a zone).
Part (b) of FIG. 23 is an enlarged view of one sector 2306.
The sector 2306 is obtained by dividing the first recording track 2303 and the second recording track 2304 by the addresses 2307. The respective sectors have the same angle (an angle on polar coordinates whose origin is the center of the optical disk) in each zone, and data having the same volume of information (e.g., the number of bits) are recorded in the respective sectors.
One sector 2306 is comprised of the addresses 2307 and the-data recording area 2308 (the first recording track 2303 or the second recording track 2304) which is sandwiched by the addresses 2307.
In part (b) of FIG. 23, the first recording track 2303 is formed in the ditch portion, while the second recording track 2304 is formed in the inter-ditch portion which is sandwiched by the ditch portion.
During tracking of a light beam, tracking control is executed in such a manner that the intensity of primary diffracted light which is created by diffraction caused by the ditches and is contained in reflected light from the disk will be balanced, whereby an optical pickup is positioned at the center of the ditch portion or the center of the inter-ditch portion. There are two points at which the primary diffracted light is balanced, one that the light beam comes falling on the ditches on the first. recording track 2303 and the other that the light beam comes falling on between the ditches on the second recording track 2304. However, since the primary diffracted light shows different polarities along the traveling direction of the light beam at these two points, by means of switching of the polarity during the tracking control, it is possible to easily switch between a state that the light beam is controlled to fall on the first recording track 2303 and a state that the light beam is controlled to fall on the second recording track 2304.
However, since the tracks of the first recording track (which is located in the ditch portion, and provided on the right-hand side and the left-hand side to which are the inter-ditch portion) and the second recording track (which is located in the inter-ditch portion, and provided on the right-hand side and the left-hand side to which are the ditch portion) alternate every round on the disk but are continuous to each other, it is necessary to inverse the tracking polarity at a point of transition from the first recording track to the second recording track and a point of transition from the second recording track to the first recording track. As marks to detect these switching points, inversion marks 2309 are provided in switching portions between the first recording track and the second recording track.
An optical disk. drive (which generally refers to recording apparatuses or reproducing apparatuses for optical disks, in which context recording apparatuses include recording and reproducing apparatuses and reproducing apparatuses include recording and reproducing apparatuses) detects the inversion marks 2309 and inverses the tracking polarity.
In the optical disk shown in FIG. 23, recorded data are modulated by the 1-7 modulation method. Since 1-7 marks (data modulated by the 1-7 modulation method.) permit retrieval of a clock necessary for demodulation from the data themselves, it is possible to demodulate and reproduce continuous data recorded in the recording area.
Part (c) of FIG. 23 shows a general structure of the address 2307.
The address 2307, which is added for identification of the sector 2306 and provision of position information on the optical disk, is comprised of a sector mark 2310 which indicates that this is the address area, a VFO mark 2311 which is used to generate a clock for reproduction of the address 2307, an address mark 2312 which expresses the beginning of address data, a sector number 2313, a track number 2314 and an error detecting code 2315.
The address is consisting of a pit (which is a concave or a convex formed on the optical disk).
Since the sector mark 2310 and the address mark 2312 are data patterns for identifying the beginning of the address data, these need be special patterns which would not appear in the sector number 2313, the track number 2314 and the error detecting code 2315.
To this end, the address data in 2313, 2314 and 2315 are recorded after bi-phase modulation, run length limit modulation (RLL modulation) or the like is executed.
Data patterns not emerging from modulation rules are obtained as a result of such modulation, and therefore, distinctive data patterns not in compliance with the modulation rules are used as the sector mark 2310 and the address mark 2312.
In addition, used as the sector mark denoted at 2310 is a mark which is sufficiently long so as to permit easy identification of the beginning of the address area even when a PLL (Phase Lock Loop) clock for synchronization is not locked.
In the prior art example shown in FIG. 23, the address data are modulated by the bi-phase modulation method. Bi-phase modulation realizes modulation of 0 into 00 or 11 and 1 into 10 or 01.
Through this modulation, ordinary data are converted into such data in which there is no string of three or more continuous ones or zeroes. Hence, a pattern in which three or more ones or zeroes appear in a row becomes a distinctive pattern which does not comply with the modulation rules.
In the prior art example shown in FIG. 23, the address mark 2312 is 10001110 while the sector mark 2310 is 1111111100000000. These pieces of data are distinctive patterns not complying with the modulation rules, and as such, can be distinguished from ordinary data.
A method of reproducing the address 2307 in the prior art example will now be briefly described.
First, the sector mark 2310 is detected. The sector mark is a distinctive pattern in which there is a string of eight continuous ones and zeroes, and therefore, using a self-driven clock of a PLL and detecting a mark whose length is equal to or longer than a certain length, it is possible to easily detect the sector mark 2310.
Upon detection of the sector mark 2310, a PLL clock for address demodulation is locked in the subsequent VFO 2311.
After locking of the PLL clock, ones and zeroes of reproduction data are judged referring to the PLL clock, thereby yielding judgment data.
As the pattern 10001110 which is the address mark 2312 is detected from the judgment data, the subsequent data are the sector number 2313, the track number 2314 and the error detecting code 2315. The detection of the address mark 2312 in this manner tells that the subsequent data are the sector number 2313, the track number 2314 and the error detecting code 2315 which are to be demodulated, and data demodulation is then executed.
As described above, when the address 2307 is read out, a position on the disk is specified from thus read address information using the track number 2314 which is position information at a radius and the sector number 2313 which is position information in the rotation direction, the particular sector 2306 is identified and recording or reproduction is performed. In this manner, data are reproduced and recorded based on address information which is added to a sector in the prior art optical disk.
In the optical disk shown in FIG. 23, pits on the optical disk substrate 2301 constitute the addresses 2307 and data of one sector which is a record unit are recorded for every recording area specified by one address 2307 as described above.
While the VFO pattern 2312 for clock synchronization is provided in the address portion 2308 in the prior art example above, there is a method which uses different means to obtain a clock for demodulation of address data.
A prior art optical disk of this type will now be described with reference to FIG. 24.
Part (a) of FIG. 24 shows a general overall structure of an optical disk according to a prior art example 2.
In part (a) of FIG. 24, denoted at 2401 is an optical disk substrate of polycarbonate, denoted at 2402 is a recording film, denoted at 2403 and 2404 are recording tracks, denoted at 2405 are zones which are provided by dividing the disk in accordance with a distance along the radius direction, denoted at 2406 are sectors which are provided by dividing the tracks into a plurality of portions in the circumferential direction, denoted at 2407 are addresses for identification of the sectors, and denoted at 2408 is a data recording area for recording of data.
In the optical disk shown in FIG. 24, a ditch portion (groove portion) alone is used as the data recording area, and the recording film is disposed which makes it possible to reproduce data by the DWDD scheme.
The DWDD scheme which realizes super resolution reproduction utilizing the mobility force of a magnetic wall necessitates magnetic blocking by means of a ditch. Hence, the tracking method shown in FIG. 24 is necessary for the purpose of realizing a narrow track pitch while using only the ditch portion (groove portion) as the data recording area. The first recording track 2403 and the second recording track 2404 which show different tracking polarities every round and the zones 2405 including different number of sectors in one round of the tracks are similar to those according to the prior art example shown in FIG. 23. Further, the data recording area 2408 is divided into the plurality of zones 2405 whose average recording density is constant along a distance in the radius direction, which is similar to the prior art example shown in FIG. 23.
Hence, a sector which has a distance from the front edge of the address 2407 until the front edge of the next address 2407 remains at the same angle (an angle on polar coordinates whose origin is the center of the optical disk) in each zone, which is also similar to the above-mentioned prior art example shown in FIG. 23. When tracking is to be performed using primary diffracted light from the ditch as in the above-mentioned prior art example described earlier, there is a limitation on intervals between tracks (track pitch) where only the ditch is used as the data recording area. The limitation upon the intervals between tracks is usually about λ/(n·NA).
The prior art example shown in FIG. 24 uses the sample servo method as a tracking method so as to set the track pitch to λ/(n·NA). The sample servo method is used for other purposes in addition to realization of a narrow track pitch because of a number of advantages, such as the resistance against tilting of a disk, over a method using primary diffracted light from a ditch. The sample servo method will now be briefly described.
Part (b) of FIG. 24 is an enlarged view of one sector 2406. The sector 2406 is obtained by dividing the recording track 2403 by the addresses 2407. The respective sectors have the same angle (an angle on polar coordinates whose origin is the center of the optical disk) in each zone. One sector 2406 is comprised of the addresses 2407 and a plurality of divided segments 2416 located between the addresses 2407. Regardless of whether belonging to the same zone or different zones, all sectors contain the same number of segments 2416.
Part (c) of FIG. 24 is a schematic enlarged view of one segment 2416.
One segment 2416 comprises a pre-pit area 2419 at the top and a subsequent data recording area 2420 which is consisting of a ditch. The pre-pit area 2419 includes a clock pit 2417 and a pair of wobble pits 2418. Disposed at the top of the pre-pit area 2419 is the clock pit 2417 which is for generating a window signal for sampling servo and a clock for data demodulation. This is followed by the pair of wobble pits 2418 for obtaining a signal for tracking.
In the optical disk shown in FIG. 24, tracking with a light beam is performed while sampling the amount of reflected light from the pair of wobble pits 2417. In short, the light beam irradiates a surface of the optical disk and the amount of the resulting reflected light is checked.
When the location of an optical pickup is off to the right-hand side or the left-hand side relative to the recording track, the amount of reflected light from the closer wobble pit 2418 decreases and the amount of reflected light from the farther wobble pit 2418 increases.
Hence, with tracking control performed such that the amounts of reflected light from the pair of wobble pits 2418 will be balanced out, it is possible to position the optical pickup at the center of the recording track 2403 or the recording track 2404. In this manner, since a track control signal (the wobble pit 2418) is buried as it is dispersed in a part of the disk according to the sample servo method, it is not necessary to obtain the track control signal (primary diffracted light) from the ditch unlike in the prior art example described above, and therefore, there is an advantage that it is possible to freely set the shape and the depth of the ditch of the data recording area 2420 which is comprised of the ditch.
Part (d) of FIG. 24 shows general structure of the address 2407.
The address is comprised of a pit (which is a concave or a convex formed on the optical disk).
The address 2407, which is added for identification of the sector 2406 and provision of position information on the optical disk, is comprised of an address mark 2410 which indicates the beginning of the address area, a sector number 2411, a track number 2412 and an error detecting code 2413.
As in the prior art example 1 described above, the address mark 2410 is a special pattern which would not appear in the sector number 2411, the track number 2412 and the error detecting code 2413.
The prior art example shown in FIG. 24, too, requires to modulate address data by the bi-phase modulation method and uses 10001110 as the address mark 2410, as in the prior art example described earlier. Since the data 10001110 are a distinctive data pattern which is not in compliance with the modulation rules of bi-phase modulation, it is possible to detect the address mark 2410.
A method of reproducing an address portion in this prior art example will now be briefly described.
First, the clock pit 2417 is detected. N-fold multiplication performed by a PLL using this clock pit generates a PLL clock for address demodulation.
As in the prior art example described above, ones and zeroes of reproduction data are judged at the fall of the PLL clock, thereby yielding judgment data.
As the pattern 10001110 which is the address mark 2410 is detected from the judgment data, the subsequent data are the sector number 2411, the track number 2412 and the error detecting code 2413.
The detection of the address mark 2410 in this manner tells that the subsequent data are the sector number 2411, the track number 2412 and the error detecting code 2413 which are to be demodulated, and data are then recorded or demodulated.
As in the prior art example described above, in this sample servo method as well, when the address is read out, a position on the disk is specified from thus read address information using the track number which is position information at a radius and the sector number which is position information in the rotation direction, a particular sector is identified and recording or reproduction is performed. In this manner, data are reproduced and recorded based on the address information which is added to the sectors.
As described above, in the optical disk shown in FIG. 24, pre-pits are formed on the addresses 2407 and the pre-pit areas 2419 on the optical disk substrate 2401 and data of one sector which is a record unit are recorded for every recording area specified by one address 2407.
As described above, in a prior art disk medium, the length or the angle of a recording track in one sector is determined in advance by a pre-pit or the like (i.e., by pre-formatting) on the disk. In other words, addresses comprised of pre-pits determine the lengths or the angles of recording tracks for every sector. In a similar fashion, addresses comprised of pre-pits and pre-pit areas determine the number of segments in each sector and the lengths of the recording tracks in each segment.
The capacity of an optical disk is determined by the total number of sectors in each zone and the optical disk has physical zone and sector structures which are pre-formatted, and therefore, it is extremely difficult to change the size of the sectors, the number of the sectors and the like on the optical disk.
Hence, even though it becomes possible to record and reproduce at an even higher density owing to an improved characteristic of a recording film of an optical disk realized by technological advance, it is not possible to increase the data capacities of optical disks which comply with an existing standard.
In order to increase the data capacities of optical disks, it is necessary to newly establish a new standard regarding optical disks and manufacture optical disks (wherein a new sector size or a new sector count is pre-formatted) which comply with the new standard.
This poses a problem that in the event that high-density optical disks are commercialized in accordance with the new standard, it would not be possible to record data in a new optical disk or reproduce data from a new optical disk using disk drives which are already available in the market since the disk drives already available in the market would not be compatible with the new format. In the case of a prior art optical disk, since a limit on a recording density is dependent upon λ/(2·NA) (where NA is the numerical aperture and A is the wavelength of reproduction light) which expresses the size of a light beam (i.e., the diameter of an area in which the intensity of the light beam is a half a peak intensity or more), for the purpose of realizing an improvement in recording density, it is essential not only to shorten the wavelength or increase the NA of a laser light source but also to enhance a capability of a recording medium. When an optical constant such as NA and λ is changed, the standard regarding optical disks needs be revised from the beginning, which obviously necessitates a change to the wavelength of a light source, a constant of a lens and the like of recording and reproducing apparatuses. Hence, the problem that it is not possible to enhance a density with the disk drives already available in the market has heretofore been considered as a problem which is strongly relevant to other problems (problems regarding optical constants such as NA and λ) and which can not be solved.
However, in the field of magneto-optical recording, the recent years have seen a number of proposals on a super resolution reproduction method which achieves a high density by means of an improvement made on a recording film without depending upon the value λ/(2·NA).
Reproduction methods according to which a recording density which permits reproduction is not dependent upon the value λ(2·NA) will be herein referred to as “super resolution reproduction methods.” Of these, the DWDD scheme (Domain Wall Displacement Detection) for reproducing recorded data which have expanded in accordance with movement of a magnetic wall is a quite excellent method according to which it is possible to reproduce a recording mark which is 0.1 μm or smaller using a light beam whose half width is approximately 0.6 μm (Japanese Patent Application Laid-Open No. 6-290496). In a magneto-optical disk utilizing such a super resolution reproduction method, it is possible to improve a recording density merely by means of an improvement in capability of the recording medium, without changing μ/(2·NA). It is possible that even the disk drives already available in the market will easily record at a high density in or reproduce at a high density from a super resolution reproduction recording medium of the DWDD type or the like as long as the recording medium has an enhanced capability.
However, as described earlier, since there are pre-formatted zones and addresses in a prior art optical disk described above, it is not possible to change the sizes of sectors which are each associated with each one of the addresses or the number of the sectors. Because of this, despite an improvement in capability of a recording film of a recording medium, the improvement in capability of the recording medium fails to be reflected when the format of the disk medium remains the same and it is therefore extremely difficult to easily increase a recording density, thus making it necessary to change the disk standard (or replacement of optical disk drives to users).
Further, information such as pre-formatted addresses is engraved on an optical disk in the form of convexes and concaves. A recording density of these pits is under a certain restriction by a limit to reproduction dependent upon the value λ/(2·NA). Meanwhile, use of the super resolution technique such as the DWDD scheme lifts off the restriction exerted by λ/(2·NA)from a recording density in a data portion. This in turn leads to the following problem.
For instance, considering a sector in which addresses have 40 bytes and data have 2048 bytes, in the case of a prior art optical disk (a medium which does not utilize a super resolution reproduction method), a recording density in an address portion (an area where there are addresses recorded) is 0.5 μm/bit and a recording density in a data portion (an area where there are data recorded) is approximately 0.5 μm/bit.
In this case, the proportion of address data to the entire data (which is called the “address redundancy”) is 0.5×40×8/(0.5×(40+2048)×8)=1.91%.
In the case of an optical disk utilizing a super resolution reproduction method such as the DWDD type (or the CAD type, the FAD (Front Aperture Detection) type or the RAD (Rear Aperture Detection) type, etc.), while a recording density in an address portion is 0.5 μm/bit, a recording density in a data portion is about 0.1 μm/bit, and hence, the address redundancy greatly increases to 0.5×40×8/((0.5×40+0.1×2048)×8)=8.9%.
The poor format efficiency is attributed to a format structure of the prior art optical disk in which one address is added to one sector.
This is also a big problem against realization of a high-density optical disk of a super resolution reproduction met hod.
Meanwhile, in the case of an optical disk having a zone structure, when accessing to a zone boundary is to be achieved, eccentricity of the disk, a seek error or the like makes it impossible to accurately move to a target zone in one seek operation. When it is impossible to move to a target zone, processing in a drive becomes very much complex and a seek time increases.
For example, in part (a) of FIG. 23, while the addresses 2307 are aligned along the radius direction within the zones, the addresses 2307 are not aligned along the radius direction between the adjacent zones.
Because of this, as the optical pickup moves back and forth between two adjacent zones, the optical pickup loses address information every time the optical pickup switches between the zones and it becomes necessary to-search for the addresses 2307 from the beginning. This tremendously slows down detection of the addresses 2307.
A prior art approach in light of this for a situation that an optical pickup needs to access a sector which is within a zone next to the current zone but which is in the vicinity of the boundary between the current zone and the next zone is a method according to which the optical pickup moves over an extra distance in advance considering even a seek error so as to be able to move to a desired zone without fail, and the optical pickup then jumps over a track from that position and moves to a desired recording track.
As described above, there is a problem that a seek time for accessing a zone boundary becomes long in an optical disk which has a zone and a sector structures which are pre-formatted in advance.
Further, there is another problem with the prior art techniques that even when one segment contained in a sector becomes defective (and hence it becomes impossible to record or reproduce), this sector as a whole becomes unusable since the sectors are in a fixed arrangement on the recording medium or since there is not spare segment in a recording area which corresponds to this sector.